Foamed styrene resin moldings are a useful material because they not only are relatively inexpensive and can be produced through foaming by low-pressure steam or other means without using a special method, but also are highly effective in cushioning and thermal insulation.
In some application, however, there are cases where the mechanical strength of :foamed styrene resin moldings is still insufficient. If the strength thereof is improved by using a nucleating agent or the like to reduce the cell size of pre-expanded styrene resin beads from which a styrene resin foam is produced, this disadvantageously results in a molding having a melted surface structure and hence an impaired appearance. On the other hand, if the cell size is increased so as to improve appearance, this results in problems including insufficient mechanical strength. Thus, a foamed molding which combines a good surface appearance and sufficient mechanical proerties including impact strength has not been obtained so far.
A technique for improving surface appearance without considerably sacrificing mechanical strength is disclosed in, e.g., JP-A-63-69843, JP-A-63-69844, and JP-A-1-299843, which technique comprises producing expandable styrene resin beads and then forcibly eliminating a foaming agent present around the bead surfaces. (The term "JP-A" as used herein means an "unexamined published Japanese patent application".)
However, the proposed treatment is industrially disadvantageous in that it needs the step of partly removing the foaming agent which has been impregnated into the expandable resin beads.